In a conventional technology, in a storage system in which a computer serving as a host and two storage apparatuses each having a RAID function are communicably connected to each other, a process and function of data redundant writing (doubling) from a host are achieved. In the redundant writing, the same data is written from the host into the storage volumes (referred to as first and second volumes) of the two storage apparatuses (referred to as first and second storage apparatuses). By doing so, a state where data is doubled (duplicated) can be maintained.
In the storage system, such a redundant writing function from the host contributes to data redundancy and improvement in reliability, which is and will be an effective function.
As the redundant writing function associated with the functions of the storage apparatus and the storage system, for example, a function of automatic return to a redundant writing state from a failed state has not been provided.
In the above-mentioned storage system, a redundant state may be changed to a non-redundant state due to a failure or the like in one of two data I/O systems (hereinafter referred to as first (primary) and second (secondary) systems) in which the redundant writing is performed. The redundant state is a state where the data contents of the first and second volumes are approximately identical to each other and are synchronized with each other. The non-redundant state (in other words, a single state) is a state where the data contents of the first and second volumes are different from each other and are not synchronized with each other.
In the control of the redundant writing, when the state is changed from the redundant state to the non-redundant state, it is necessary to return the state to the redundant state through some procedure. In the non-redundant state, a difference occurs between the data contents of the first and second volumes. Therefore, concurrently with recovery of the failed portion, a process of synchronizing the data contents of the first and second volumes is required.
Japanese Patent Laid-Open Publication No. 7-36629 (Patent Document 1) discloses a recovery processing method for failure recovery at the time of occurrence of a failure in redundant disk devices.